The invention relates to an ion source of the Penning discharge type, and more particularly to a Penning discharge ion source with a self-cleaning aperture.
The problems of vaporizing materials at a high temperature in order to produce ions of the material are avoided by using the Penning (oscillating electron) discharge with a cold sputter electrode disposed between cathodes as disclosed in U.S. Pat. No. 3,566,183 by Basil F. Gavin, one of the present inventors, and reported by him in a paper titled "A Sputtering Type Penning Discharge For Metallic Ions," Nuclear Instruments and Methods 64 (1968) at pages 73-76.
An offspring of the Penning discharge ion source described in that patent and paper has been successfully used. That offspring is described in detail hereinafter with reference to drawings. Although it solved one problem, it created another problem, namely that the exit slit for the ions tends to become clogged. This occurs for two reasons: some of the atoms move directly from the sputter electrode to the exit slit and deposit there, and ions are neutralized and deposited on the slit. Clogging the slit renders the ion source inoperative until a new slit is provided, and the deposited material which clogs the slit is lost, thus reducing the lifetime of the ion source. Reliable and long lifetime sources are necessary for particle accelerators for atomic and nuclear research, and as sources of heavy ions for biomedical applications and cancer therapy. They are also expected to be used extensively in future fusion energy systems.